There are demands for techniques of conducting non-destructive internal tests of test objects. For example, there is available a technique of testing the inner structure of a semiconductor by a non-destructive internal test using a laser ultrasonic device. The laser ultrasonic device irradiates the surface of a test object with a laser beam to make the object surface absorb the light, thereby making the object internally generate elastic waves. The elastic waves generated inside the object propagate inside the object. The laser ultrasonic device internally tests a test object by acquiring a signal concerning elastic waves propagating in the object.